Question: WHY were the Israelites commanded not to make graven images?

Answer: Graven images were the standard method of pagan worship. They were representations of false gods.

Now that being the case, it is fairly obvious that an 'image' NOT made for worship is acceptable. In fact, we should not really call things like the cherubim 'images' at all -- an 'image' in ancient thought is not merely something that has an appearance, like a statue or a picture, but something that serves as a focal point for the presence and power of a deity.

Thus for example ancient rulers in Egypt, Babylon, and elsewhere were referred to as the 'image' of a certain deity, not because they looked like the deity, but because the deity's power and authority was thought to operate through them. To interpret these passages otherwise is to adopt a rigid interpretation that misses the context of ancient worship practices. (It is understandable, however, as an instance of erring on the side of caution, which characterized much of later ancient Jewish culture's avoidance of all art.)

Solomon's bulls and such were (as far as we can tell) not for worship and do not fit the definition of an 'image' we have described. The cherubim on the Ark were not for worship and also do not fit the ancient definition. So, the command was not violated in either case.

We should add that the Hebrew words for 'image' and 'likeness' are essentially synonyms (as shown both by their interchangeable use in the OT, and by the interchangeable use of the equivalent words in pagan literature of the period), and a 'likeness' is also therefore a focal point for the presence and power of a deity, just like an image.